Proposition de sujet de thèse

Proposition de sujet de thèse
2014
Intitulé du sujet
Directeur
de thèse
Co-Directeur
de thèse
Laboratoire d'accueil
Towards realistic seismic cycle model: Postseismic, interseismic and
multi-cycle deformation data contribution
Nom Prénom
Bouissou Stéphane
Unité de recherche
Géoazur UMR 7329
Téléphone
04.83.61. 86.69
Courriel
[email protected]
Nom Prénom
Vergnolle Mathilde
Unité de recherche
Géoazur UMR 7329
Téléphone
04.83.61. 86.27
Courriel
[email protected]
Géoazur UMR 7329
Bâtiment 4
250 rue Albert Einstein
Sophia Antipolis
06560 VALBONNE - France
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Proposition de sujet de thèse Géoazur 2014
DESCRIPTION DU SUJET
Towards realistic seismic cycle model:
Postseismic, interseismic and multi-cycle deformation data contribution.
It has long been thought that large earthquakes are separated by a long quiescent
interseismic period in which stresses, relaxed by a preceding earthquake, are restored under
the constant tectonic loading induced at plate boundaries. This idea gives birth to the ‘elastic
seismic cycle’, as defined after the 1906 San Francisco earthquake. This physical model,
widely tested and validated at the first order over numerous observations, is still used in the
community as it provides a simple framework for studying earthquakes and faulting.
However, an increasing number of observations indicate that additional processes, such as
postseismic stress relaxation, are involved in the build-up and relaxation of crustal stress.
Postseismic deformation is thought to play an important role in modulating the occurence of
seismic sequences after a principal event. Postseismic stress relaxation may also explain
delayed earthquake triggering, due to its time-dependent evolution over various time scales
(see Freed, 2005, for a comprehensive review). More observation and insight on postseismic
processes will ultimately allow us to better integrate them into more complex seismic cycle
models to try to better reproduce past earthquake history. From this, we can then look
forward in time, thus improving the way we assess seismic hazard, and define which faults
are subject to rupture during an earthquake sequence. Another issue to understand the
behavior of fault and surrounding medium over the course of a seismic cycle period (lasting
several 10-100yrs) is the lack of observations covering it entirely. The longest available
measurements usually cover about 10 yrs and as such solely represent a short instant of the
entire seismic cycle.
The objective of the project are (1) to extend the temporal range of observations combining
new and more traditional spatial geodetic tools and data to document the longest period of
the seismic cycle as possible, (2) to implement more realistic models of the seismic cycle
including postseimic relaxation, and (3) to validate these models with the multi-scale
observations obtained previously.
Seismic cycle deformation will be measured using complementary geodetic datasets,
including InSAR, GPS and optical image correlation. The objective is to document and
provide a complete description of several periods of the seismic cycle on a fault system. The
PhD student will be mainly in charge of processing optical images using new sub-pixel
correlation methods (e.g. Copley et al., 2012). In particular, this technique has the great
advantage of enabling us to quantify earthquake deformation during the pre-InSAR/GPS time
period, for which little is known, using existing old and more recent aerial photos
(Hollingsworth et al., 2013, 2012).
Theoretical models suggest that postseismic deformation driven by viscoelastic relaxation
could persist for several tens to several hundreds of years (Pollitz, 1997). Moreover,
viscoelastic relaxation processes are believed to be an essential component of fault system
behavior and important for bringing major fault zone cycles of neighboring faults into
synchroneity (Chéry et al., 2001). The objective of the project is to bring elements to validate
these hypothesis that have not been tested in numerous real cases. The PhD student will
particularly focus on the implementation of models based on the elastic dislocation theory for
a viscoelastic layered Earth (Pollitz & Vergnolle, 2006; Barbot & Fialko, 2010). The PhD
student will explore which model parameters (such as varying rheologies, friction
parameters, fault geometries, etc) need to be refined to reproduce the multi-scale geodetic
mesurements of the surface deformation that integrate both coseismic, short- and long-term
postseismic and interseismic deformation. Based on this understanding, the PhD student will
whether or not the new model(s) may account for some of the major strong earthquake
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Proposition de sujet de thèse Géoazur 2014
clusters observed within large-scale fault systems. This work should improve our
understanding of the effects of delayed stress loading on faults within fault systems.
We will focus on the 1968-1997 earthquake sequence in East Iran (1968 Mw 7.1 Dash-eBayaz, 1979 Mw 7.1 Khuli-Buniabad, and the 1997 Mw 7.2 Zirkuh earthquakes). Using
optical data, we will examine the 1968 and 1979 earthquakes, while optical and InSAR data
are available for the 1997 earthquake (Sudhaus, et al., 2011). We will also benefit from a
regional GPS velocity field and a regional detail fault map (Walpersdorf et al., 2014) to
parametrerize the models.
Expertise requested: The candidate will work at the interface between numerical modeling
(development of the seismic cycle models) and spatial geodesy. A background in geophysics
and active tectonics would be appreciated, while skills in numerical modeling are requested.
Connaissances et compétences requises :
Le candidat travaillera à l’interface entre modélisation numérique et géodésie spatiale. Il
devra posséder un bagage solide en géophysique et des capacités en implémentation
numérique. Un candidat issu d’une formation initiale (Licence) mathématique ou physique et
possédant un Master en Géophysique serait de fait approprié. Le candidat sera intégré dans
une équipe pluri-disciplinaire (géodésie- tectonique-sismologie-modélisation) et devra se
familiariser avec les différentes données issues de ces disciplines afin de les intégrer dans
les modélisations.
Bibliographie :
Barbot, S., Fialko, Y., 2010. A unified continuum representation of post-seismic relaxation
mechanisms : semi-analytic models of afterslip, poroelastic rebound and viscoelastic flow :
Semianalytic models of postseismic transient. Geophys. J. Int. 182, 1124–1140.
Chéry, J., Merkel, S., Bouissou, S., 2001. A physical basis for time clustering of large
earthquakes. Bull. Seism. Soc. Am. 91, 1685–1693.
Copley, A., Hollingsworth, J., Bergman, E., 2012. Constraints on fault and lithosphere
rheology from the coseismic slip and postseismic afterslip of the 2006 Mw7. 0 Mozambique
earthquake. J. Geophys. Res. Solid Earth 1978–2012 117.
Freed, A.M., 2005. Earthquake triggering by static, dynamic, and postseismic stress transfer.
Annu. Rev. Earth Planet. Sci. 33, 335–367.
Hollingsworth, J., Leprince, S., Ayoub, F., Avouac, J.-P., 2012. Deformation during the 1975–
1984 Krafla rifting crisis, NE Iceland, measured from historical optical imagery. J. Geophys.
Res. Solid Earth 1978–2012 117.
Hollingsworth, J., Leprince, S., Ayoub, F., Avouac, J.-P., 2013. New constraints on dike
injection and fault slip during the 1975-84 Kraa rift crisis, NE Iceland. J. Geophys. Res. Solid
Earth 118, 3707– 3727.
Pollitz, F. F., 1997. Gravitational viscoelastic postseismic relaxation on a layered spherical
Earth. Journal of Geophysical Research: Solid Earth (1978–2012), 102(B8), 17921-17941.
Pollitz, F.F. and Vergnolle, M., 2006. Mechanical deformation model of the western United
States instantaneous strain-rate field. Geophys. J. Int. 167, 421–444, doi: 10.1111/j.1365246X.2006.03019.x.
Walpersdorf, A., Manighetti, I., Mousavi, Z., Tavakoli, F., Vergnolle, M., Jadidi, A., Hatzfeld,
D., Aghamohammadi, Bigot, A., Djamour, Y., Nankali, H., Sedighi, M., accepted 2014.
Present-day kinematics and fault slip rates in Central-Eastern Iran, derived from 11 years of
GPS data. J. Geophys. Res.
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Proposition de sujet de thèse Géoazur 2014
Collaborations internes :
James Hollingsworth, co-directeur
Olivier Cavalié, collaborateur
Collaborations externes :
A. Walpersdorf (ISTerre)
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